Improved land-atmosphere relations through distributed footprint sampling in a subtropical scrubland during the North American monsoon

The relation between land surface states and fluxes is fundamental for quantifying the ecohydrological controls on the North American monsoon. In this study, we utilize distributed sampling around an eddy covariance tower in Sonora, México, to evaluate the impact of footprint variations in soil moisture (θ) and temperature (Ts) on surface flux partitioning. Results indicate that spatial variability is important to capture when θ or Ts have a high spatial mean and control the dominant surface flux, either latent (λE) or sensible (H) heat. As a result, we found that θ and Ts measurements at the tower may not be representative of the footprint-averaged states, with larger discrepancies for Ts due to the radiative heterogeneity. Using the spatially-averaged land surface conditions in the footprint moderately improves the relations with the surface fluxes as quantified by the Bowen ratio (B) and the evaporative fraction (EF). To our knowledge, this is a first attempt to address the scale discrepancy between aggregated flux measurements from an eddy covariance tower and the effective land surface states within the footprint through distributed sampling. Improvements in land-atmosphere relations are more significant for footprint conditions exhibiting high spatial variability or a large bias as compared to the tower site measurements. © 2009 Elsevier Ltd. All rights reserved.